The information gained is expected to give new insights into the steroidal regulatory mechanism(s) affecting the hypothalamic-ovarian axis, which might ultimately reveal new avenues for the control of fertility. This part year and presently our group has explored at both hypothalamic and hypophyseal levels such aspects as: 1. The metabolism of progesterone and 20%-dihydroprogesterone by the hypothalamus and anterior pituitary and their uptake and binding. These investigations have and should continue to provide the bases for subsequent investigations of the mode and nature of the binding steroidal and macromolecular species. 2. The subcellular localization of the gonadotropin releasing factor(s). These investigations have already provided the basis for subsequent experiments in elucidating the sequential scheme of events from sex steroid feedback - uptake yields hypothalamic gonadotropin releasing factor release and/or inhibition (or pituitary).